
====== MBMixer ======

{{pga:mbmixopen.jpg}}

===============================================================================
Copyright (C) 2007  Lyle Hazelwood (lylehaze@bellsouth.net)
Licensed for personal non-commercial use only.
All other rights reserved.
===============================================================================
<description>
Drives an audio mixer built with PGA2311 or PGA4311 volume controls.
===============================================================================
<overview>
This project provides a digitally controlled analog audio mixer. Using either 
an encoder or MIDI control messages, the user may control the volume and 
balance of attached audio sources.

===============================================================================
<hardware> This project is built around the MIDIBox core module, which is a PIC18F452
based MIDI device. Additionally, a DINX1 may be used (optional) to connect an
encoder and pushbutton. A display module may optionally be connected. The one I
designed for is 2 lines X 20 characters, but it's not difficult to change. Some 
quantity of PGA2311 and/or PGA4311 chips are needed to control the audio levels.
The 2311 chips support 2 audio channels each (one pair), and the 4311 chips 
support four audio channels (two pairs). A NE5532 dual op-amp based summing 
circuit is used to combine the audio sources, and NE5532 based input buffers may
also be used to assure that the inputs have a sufficiently low impedance. 
Finally, a power supply provides unregulated +V to the MidiBox, also two +5 volt
and one -5 volt regulators to supply the PGA chips and audio circuits.

Additional Hardware Info: [[MIDIboxMixerHardware]]


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<software>
The entire project is designed within MIOS, which is a fantastic open sourced
OS for embedded MIDI applications that is written and maintained by Thorsten 
Klose. The actual code to control the PGA chips was based on code provided by
Pilo, who provided it after chatting with him at www.midibox.org/forum/index
The MIOSMix application can handle up to 16 pairs of audio. the level of each
pair is controlled by MIDI volume controls, also known as Control Change #7.
We also consider MIDI control change #8, Balance. The valid range for each of
these is 0 to 127. For Volume, 0 is muted, and 127 is _VERY_ loud. For the 
Balance control, 0 or 1 gives Full Left, 64 is centered, and 127 is full Right.
As controls matching these are received, they are applied to the PGA settings,
and are also displayed on the Display, if equipped.

The reference design has only a single encoder with pushbutton. The user may
select the channel by pressing the button, then turn the encoder to adjust the
level. any changes made with the local encoder are also sent out the MIDI out
port, so that the control deck can stay synchronized with the actual level.
It would be a simple modification to support a separate encoder for each 
channel, if more complete local controls are desired.

Software Configuration info: [[MIDIboxMixerSoftware]]


===============================================================================

An Operators manual for the MBMixer:
[[MIDIboxMixerManual]]
